The invention relates to an actuator arrangement for applying a torque to a shaft of a machine, in particular a crankshaft of a reciprocating piston engine. The invention relates to a corresponding method.
Machine shafts such as crankshafts in reciprocating piston engines are subject to torque irregularities, known as rotary oscillation or torsional vibration due to intermittent drive torques.
Rotary oscillations of such kind can be reduced with passive systems, such as torsional vibration dampers (also called “visco dampers” with viscous medium), equipped with an inertia ring. Examples of these are described in EP 1266152B1, U.S. Pat. Nos. 6,026,709A, and 5,637,041 A.
German patent document DE10 2010 046 849 B4 describes a sensor-based control of vibration in slender continua, specifically torsional vibration in drill strings. A theory for calculating working shaft on the basis of two measurement points is presented.
Other active systems for vibration damping with an actuator are known from DE 195 32 129 A1 and DE 103 04 559 A1. In the latter document, an actuator acts on a transmission of a vehicle powertrain which is connected downstream of a reciprocating piston engine crankshaft via a dual mass flywheel. However, due to the decoupling effect of the dual mass flywheel it is not possible to reduce or excite vibration in the crankshaft.
Document WO 2014/118245 A1 describes an active system for vibration damping which includes an actuator. The shaft of WO 2014/118245 A1 is a crankshaft of the reciprocating piston engine which has a front end and a driven end. The reciprocating piston engine may be for example a diesel, gasoline or gas engine, and may be used for various purposes, as an automobile power unit for example. The crankshaft may include—preferably at a driven end—a flywheel, a dual mass flywheel for example, to which a powertrain of an automobile having a drive transmission is connected downstream.
A torque is applied to a shaft of an internal combustion engine to start the machine, typically by means of a starter motor. In the case of hybrid machines in automobiles, the electric motor of the hybrid machine can also be used for this. This electric motor may be switched into a generator mode for braking, in which case the electric motor then produces electrical energy as a generator.
The need for effective damping devices is constant, not only to prolong the service life of the parts affected by vibration, but at the same time also to reduce maintenance costs.
The object of the present invention therefore consists in providing an improved actuator arrangement and an improved method for applying a torque to a machine shaft.
This object is solved with an actuator arrangement for applying a torque to a shaft of a machine, particularly a reciprocating piston machine, with at least the following features:
a) at least one actuator device for applying for torque,
b) at least one rotatable seismic mass coupled with the shaft,
c) wherein the at least one actuator device is designed to apply the torque between the seismic mass and the shaft. This object is also solved with a method for applying a torque to a shaft of a machine, in particular to a crankshaft of a reciprocating piston machine, with the above actuator arrangement, with the method including the steps of:
(S1) detecting a requirement for torque;
(S2) determining actuation data for the at least one electrical machine on the basis of the requirement for torque detected; and
(S3) applying the torque to the shaft by actuating the at least one electrical machine to drive the at least one actuator device.
Accordingly, an actuator arrangement according to the invention for applying a torque to a shaft of a machine, in particular a reciprocating piston engine comprises a) at least one actuator device for applying the torque, and b) at least one rotatable seismic mass coupled to the shaft, c) wherein the at least one actuator device is designed to apply the torque between the seismic mass and the shaft.
A “seismic” mass is a physical mass which in this case becomes a “seismic” mass by virtue of its construction, e.g. as an inertia ring, arrangement and coupling, as is known from vibration measurement technology. The seismic mass in the form of a flywheel and/or inertia ring is connected to a rotatable body, in the present case a shaft, and rotates with it at the same rotating speed. In a passenger car, a moment of inertia I of such a seismic mass is in a range from e.g. 0.01 to 0.5 kgm2, in a commercial vehicle in a range from e.g. 0.1 to 3 kgm2, in a stationary machine (EPG) in a range from e.g. 3 to 100 kgm2 and in a large two-stroke internal combustion engine in a range from e.g. 100 to 35,000 kgm2. The seismic mass forms a practically absolute reference system with regard to the shaft, with respect to which differences from the rotating speed of the shaft are induced, caused for example by rotary oscillations from a shaft drive system, e.g., a reciprocating piston engine. The shaft is therefore preferably a crankshaft of a reciprocating piston engine and the at least one actuator device is designed to apply a torque between the seismic mass and the crankshaft of the reciprocating piston engine.
The advantage of the co-rotating seismic mass consists in the low speed differentials between the shaft and the seismic mass. In other words, the speed differential between the shaft and the seismic mass results solely from the rotary oscillation superimposed on the uniform rotation of the shaft and the seismic mass. In this context, the term speed is understood to refer to rotating speed.
A method according to the invention for applying a torque to a shaft of a machine, in particular a crankshaft of a reciprocating piston engine, in particular with the actuator arrangement according to the invention, comprises the method steps (S1) detecting a requirement for torque; (S2) determining actuation data for the at least one electrical machine on the basis of the detected requirement for torque; and (S3) applying the torque to the shaft by actuating the at least one electrical machine to drive the at least one actuator device.
The actuator device according to the invention is particularly suitable for damping rotary oscillations of the shaft, wherein the method according to the invention for active damping of rotary oscillations of the machine shaft provides in method step (S1) for detecting rotary oscillation information relating to the shaft with the at least one measuring device, in method step (S2) for determining actuation data for the at least one electrical machine on the basis of the detected input data, and in method step (S3) for active damping of the rotary oscillations of the shaft by actuating the at least one electrical machine to drive the at least one actuator device.
Thus, the actuator device according to the invention offers a significant advantage in that it is capable of combining various applications for applying the torque to the shaft. For example, the application of torque may be used for an acceleration process, e.g., a starting process for an engine to which the shaft is attached, for a braking process and to damp rotary oscillations of the shaft.
In a further variant, the actuator arrangement is designed to apply an alternating torque to the shaft. The term “alternating torque” is defined as follows.
With alternating torque, the torque curve crosses the zero line from positive values to negative values and vice versa. Of course, this curve may also be periodic, damped or undamped, or even cumulative in certain time intervals. Such an alternating torque is applied to a shaft particularly for damping rotary oscillations thereon.
If the torque were applied to damp the rotary oscillations between the rotating shaft and an immobile reference point, the dissipated output with a viscous damper would be very high, since the damper would also decelerate the uniform rotary motion.
If an active system with an actuator such as is described in the prior art is to be used to damp rotary oscillations of the shaft, one possible variant for an actuator would be the use of an electric motor with a fixed stator and a rotor secured to the shaft on which the rotary oscillations occur. In this context, it is considered disadvantageous that the electric motor requires a very high nominal output. This is calculated with the formula P=Mw wherein M stands for the required torque and co for the angular velocity of the shaft. Since the alternating torque needed to damp the rotary oscillations in internal combustion engines is typically in the same order of magnitude as the nominal torque of the internal combustion engine, the actuator would have to be capable of delivering a nominal output in the same order of magnitude as the internal combustion engine. This is not conceivable except for special applications (hybrid, generator). However, with a rotor that co-rotates at the same speed as the shaft, the energy required to supply the actuator would have to be transferred contactlessly.
A defined alternating torque may be applied to a rotating shaft to reduce rotary oscillations or to generate rotary oscillations. In fulfillment of the law that states “For every action there is an equal and opposite reaction”, it follows that this torque must be counterbalanced. To address this, two suggested solutions are to support this torque a) against a spatially fixed point or b) against a co-rotating seismic mass.
If the actuator of this torque were an electric motor, for example, in the case of a) the stator of the electric motor would be spatially fixed, and in the case of b) the stator of the electric motor would be secured on the co-rotating seismic mass.
In the case of a), the problem arises that the engine output delivered at any given time P(t) can be very high. If the shaft is rotating with an angular velocity and an alternating torque to be applied has a certain value, a current output P(t) may have an average value of zero, but the electric motor must still be of correspondingly large dimensions.
This may be explained more clearly with an example. In order to reduce vibration in the crankshaft of a truck internal combustion engine, an alternating torque of
2 kNm must be applied for a rotating speed of 1800 rpm. As a result, the amplitude of the current power output from the electric motor is approximately 377 kW. An electric motor capable of delivering this power is big, heavy and expensive.
This problem does not exist in case b), since the stator and the rotor of the electric motor are rotating at almost the same speed due to the co-rotating seismic mass. However, in this case the supply of electrical power to the electric motor via slip rings (wear, maintenance) and inductive processes presents a significant disadvantage. Furthermore, here too the actuator (an electric motor in the example) must apply the alternating torque of 2 kNm, which requires a correspondingly large, expensive electric motor and is also unfavorable.
In contrast to the above suggestions, the invention solves the aforementioned difficulties associated with avoiding the drawbacks of a) and b) as follows, with a) at least one actuator device for applying a torque serving in particular to damp rotary oscillations of the shaft, and b) at least one rotatable seismic mass coupled with the shaft, c) wherein the at least one actuator device is designed to apply the torque for damping rotary oscillations of the shaft between the seismic mass and the shaft.
The torque for damping rotary oscillations of the shaft is applied between the seismic mass and the shaft by the at least one actuator device. This forms and preferably creates a coupling between the seismic mass and the shaft. In this way, the torque that is to be applied to the shaft to excite or reduce rotary oscillations of the shaft can be applied simply and in suitable manner.
One variant provides that the rotatable seismic mass is coupled with the shaft in such manner that the rotatable seismic mass rotates at the same rotating speed as the shaft. This enables the torque that is to be applied to the shaft to damp rotary oscillations of the shaft to be kept small. However, it is also conceivable to enable co-rotation of the seismic mass sometimes at the same speed and sometimes at a different speed depending on the operating state.
The actuator arrangement has at least one electrical machine for supplying driving energy for the at least one actuator device. An electrical machine of compact construction can be produced quite simply.
In one variant, the actuator arrangement includes at least one transmission, via which the at least one actuator device is coupled to the at least one electrical machine to receive its driving power. A transmission enables a particularly large number of options for applying alternating torque to a rotating shaft according to each individual application case.
In a further variant, the at least one transmission and the at least one actuator device are disposed on the at least one seismic mass. This enables a particularly compact construction.
It is provided that the transmission has a housing, which is fixedly connected to the seismic mass. This advantageously ensures that a transmission ratio can be created between the rotating speed of the seismic mass and the electrical machine in order to reduce the rotating speed and driving power of the electrical machine. Such a housing may provide bearing points and/or fastening points for transmission components, for example. Consequently, the transmission can be installed simply as single unit and easily replaced during maintenance operations. This also enables a compact construction.
In a further variant, the rotatable seismic mass and the electrical machine together with the shaft have the same axis of rotation, which simplifies the construction.
This also offers the advantage that the power output from the electrical machine can be kept relatively low (about 5 kW for a truck engine), and a required installation space is also relatively small.
In this context, in one variant it is provided that the at least one electrical machine has the form of an electric motor with a stator and a rotor, wherein the stator is fastened in fixed manner to a frame and the rotor is coupled with the at least one actuator device either indirectly via the transmission or directly. In one variant, the electric motor may be designed for a rotating speed of ±16,000 rpm. In this way, it is possible to ensure highly dynamic regulation depending on the current state of the associated machine, e.g., a reciprocating piston engine.
The stator of the electric motor is mounted fixedly on the frame, e.g., the frame of the reciprocating piston engine. The rotor drives the actuator device located on the seismic mass, which co-rotates with uniform shaft velocity.
In one variant, the transmission is a gear transmission, wherein the at least one actuator device is in the form of an output gear of the transmission, and wherein a transmission input is coupled with the rotor of the at least one electrical machine. Gearwheels as components can be manufactured in high quality and enable a relatively simple construction.
In an alternative variant, the transmission has at least one generator and at least one electric motor, wherein the at least one electrical motor functions as the at least one actuator device, and wherein the at least one generator is coupled with the rotor of the at least one electrical machine. In this context, a “gear train” may advantageously be created by designing the respective electrical machine relatively simply, with a small number of moving parts.
In a preferred variant, the transmission includes at least one pump, which is in the form of a hydraulic pump, particularly a gear pump, and the at least one actuator device, wherein the pump is coupled with the rotor of the at least one electrical machine, and wherein the at least one actuator device is in the form of a radially arranged hydraulic cylinder of the pump, a displacement vane or a gear pump.
In one variant, the at least one actuator device is a hydraulic cylinder of a pump, which is a hydraulic pump, is, wherein the pump is arranged on the seismic mass and is coupled with the rotor of the at least one electrical machine. The seismic mass and thus also the pump rotate with the uniform shaft rotation velocity, wherein the torque for damping is generated by relative acceleration between the seismic mass and the shaft. In this way, the power output of the electrical machine is relatively low, as indicated earlier.
In an alternative variant, the at least one actuator device may include one or more piezoelements or piezoactuators, wherein the transmission is equipped with at least one generator for supplying energy to the one or more piezoelements, and is arranged on the seismic mass, and is coupled with the rotor of the at least one electrical machine.
The coupling of the seismic mass to the shaft may be assured only via the at least one actuator device, as described previously, for example, or in a further variant it may be constructed such that the at least one rotatable seismic mass is also coupled to the shaft via a spring unit. The spring unit may include parallel connected springs, e.g., torsion springs, or helical springs distributed around the circumference. The seismic mass is then connected and/or coupled to a front end of the shaft via the spring unit and via cylinders of the hydraulic pump.
The hydraulic cylinders and piezoactuators may produce a defined displacement (defined acceleration or defined torque) between the seismic mass to the shaft.
In a further variant, the actuator arrangement is equipped with a device for decelerating the shaft. In this context, the device for decelerating the shaft may comprise the at least one electrical machine for recovering energy. The recovered electrical energy may be stored e.g. in an automobile battery or an additional electrical energy accumulator.
In yet another variant, it is provided that the actuator arrangement includes a device for accelerating the shaft, wherein the at least one electrical machine generates acceleration processes. In this way, assistance can be provided to the machine associated with the shaft for starting processes and/or other operating states for example.
In a further variant, the actuator arrangement includes at least one controller for controlling the electrical machine and at least one measuring device for detecting rotary oscillation information relating to the shaft, wherein the controller is designed to control the electrical machine on the basis of the rotary oscillation information for the shaft detected by the measuring device for applying a torque for damping rotary oscillations of the shaft. This enables an advantageously simple central control for the actuator arrangement, wherein the essential current measurement values relating to the rotary oscillations of the shaft can be captured and rapidly processed by the measuring device. In this way, the controller is able to control the electrical machine so that the electrical machine drives the actuator device in such manner that the actuator device applies the torque for damping rotary oscillations of the shaft to the shaft, to enable accurate and precise rotary oscillation damping (or also rotary oscillation generation) in the shaft.
The controller of the actuator arrangement may also include a regulating unit for providing a superimposed rotating speed regulation of the seismic mass. In this way, it is advantageously assured that a uniform rotating speed of the seismic mass at a given time is equal to a uniform rotating speed of the coupled shaft at the same time.
In a variant of the method, in method step (S1) provision is made for simultaneous transfer of additional information from an engine controller (16) of the machine to be assigned. The operating state of the shaft with the associated machine or reciprocating piston engine may be detected using data relating to the rotating speed and angular position of the crankshaft and the current load of the machine, thereby enabling further improvement to the damping of rotary oscillations of the shaft.
In method step (S3), a torque for damping rotary oscillations of the shaft is generated between the shaft and seismic mass which co-rotates with the shaft by the at least one actuator device by relative acceleration between the seismic mass and the shaft. Consequently, the small speed differentials mean that it is only necessary to apply a relatively low torque.
The invention will now be explained in greater detail based on an exemplary embodiment and with reference to the accompanying drawings.